Showing papers on "Inferior longitudinal fasciculus published in 2008"
TL;DR: This work establishes the critical causal role of this fiber tract in normal reading, and shows that its disruption is one pathophysiological mechanism of pure alexia, thus clarifying a long-standing debate on the role of disconnection in neurocognitive disorders.
265 citations
TL;DR: It is suggested that superficial damage to the inferior parietal cortex per se may not be sufficient to produce visual neglect, and in some cases, a lesion to the direct connections between ventral occipital and frontal regions (ie, IFOF) may contribute to the manifestation of neglect by impairing the top down modulation of visual areas from the frontal cortex.
Abstract: Left unilateral neglect, a dramatic condition which impairs awareness of left-sided events, has been classically reported after right hemisphere cortical lesions involving the inferior parietal region. More recently, the involvement of long range white matter tracts has been highlighted, consistent with the idea that awareness of events occurring in space depends on the coordinated activity of anatomically distributed brain regions. Damage to the superior longitudinal fasciculus (SLF), linking parietal to frontal cortical regions, or to the inferior longitudinal fasciculus (ILF), connecting occipital and temporal lobes, has been described in neglect patients. In this study, four right-handed patients with right hemisphere strokes underwent a high definition anatomical MRI with diffusion tensor imaging (DTI) sequences and a pencil and paper neglect battery of tests. We used DTI tractography to visualise the SLF, ILF and the inferior fronto-occipital fasciculus (IFOF), a pathway running the depth of the temporal lobe, not hitherto associated with neglect. Two patients with cortical involvement of the inferior parietal and superior temporal regions, but intact and symmetrical fasciculi, showed no signs of neglect. The other two patients with signs of left neglect had superficial damage to the inferior parietal cortex and white matter damage involving the IFOF. These findings suggest that superficial damage to the inferior parietal cortex per se may not be sufficient to produce visual neglect. In some cases, a lesion to the direct connections between ventral occipital and frontal regions (ie, IFOF) may contribute to the manifestation of neglect by impairing the top down modulation of visual areas from the frontal cortex.
202 citations
TL;DR: The hypothesis that the strategic location of white matter hyperintensities may be critical in late-life depression is supported, as well as the correlation of neuropsychological deficits with the volumes of whole brain white matterhyperintensity and gray and white matter in depressed subjects but not comparison subjects.
Abstract: Objective: Segmented brain white matter hyperintensities were compared between subjects with late-life depression and age-matched subjects with similar vascular risk factor scores. Correlations between neuropsychological performance and whole brain-segmented white matter hyperintensities and white and gray matter volumes were also examined. Method: Eighty-three subjects with latelife depression and 32 comparison subjects underwent physical examination, psychiatric evaluation, neuropsychological testing, vascular risk factor assessment, and brain magnetic resonance imaging (MRI). Automated segmentation methods were used to compare the total brain and regional white matter hyperintensity burden between depressed patients and comparison subjects. Results: Depressed patients and comparison subjects did not differ in demographic variables, including vascular risk factor, or whole brain-segmented volumes. However, depressed subjects had seven regions of greater white matter hyperintensities located in the following white matter tracts: the superior longitudinal fasciculus, fronto-occipital fasciculus, uncinate fasciculus, extreme capsule, and inferior longitudinal fasciculus. These white matter tracts underlie brain regions associated with cognitive and emotional function. In depressed patients but not comparison subjects, volumes of three of these regions correlated with executive function; whole brain white matter hyperintensities correlated with executive function; whole brain white matter correlated with episodic memory, processing speed, and executive function; and whole brain gray matter correlated with processing speed. Conclusions: These findings support the hypothesis that the strategic location of white matter hyperintensities may be critical in late-life depression. Further, the correlation of neuropsychological deficits with the volumes of whole brain white matter hyperintensities and gray and white matter in depressed subjects but not comparison subjects supports the hypothesis of an interaction between these structural brain components and depressed status.
196 citations
TL;DR: The findings, which benefited from greater image resolution and methodological control than previous studies conducted in adolescents with schizophrenia, provide strong evidence for lower white matter integrity in the left ILF, particularly for patients with a history of visual hallucinations.
99 citations
TL;DR: A framework to integrate fiber tract information from DTI-based tractographic atlases in tractwise and voxelwise lesion-deficit analyses is developed, with the potential to facilitate identification of both cortical sectors and fiber tracts critical for cognitive functioning.
87 citations
TL;DR: FA and MD values of DTI may be used as novel biomarkers for the evaluation of neurodegenerative disorders and microstructural changes of several corticocortical tracts associated with cognition were identified in patients with MCI.
Abstract: Mild cognitive impairment (MCI) has been defined as a transitional state between normal aging and Alzheimer disease. Diffusion tensor imaging (DTI) can estimate the microstructural integrity of white matter tracts in MCI. We evaluated the microstructural changes in the white matter of MCI patients with DTI. We recruited 11 patients with MCI who met the working criteria of MCI and 11 elderly normal controls. The mean diffusivity (MD) and fractional anisotropy (FA) were measured in 26 regions of the brain with the regions of interest (ROIs) method. In the MCI patients, FA values were significantly decreased in the hippocampus, the posterior limb of the internal capsule, the splenium of corpus callosum, and in the superior and inferior longitudinal fasciculus compared to the control group. MD values were significantly increased in the hippocampus, the anterior and posterior limbs of the internal capsules, the splenium of the corpus callosum, the right frontal lobe, and in the superior and the inferior longitudinal fasciculus. Microstructural changes of several corticocortical tracts associated with cognition were identified in patients with MCI. FA and MD values of DTI may be used as novel biomarkers for the evaluation of neurodegenerative disorders.
80 citations
TL;DR: DTI can be used to identify absence of AF and inadequate maturation of ILF in children with global developmental delay of unknown etiology and shows no asymmetry for these tracts in controls or developmentally delayed children.
44 citations
14 Oct 2008
TL;DR: The corpus callosum, superior longitudinal fasciculus right and inferior longitudinal Fasciculus left were found to be having high correlations with test scores, and the correlates of scalar DTI measures, such as fractional anisotropy, mean diffusivity, axial diffusiveness, and radial diffuivity with behavioral test scores were investigated.
Abstract: Abnormalities in white matter (WM) brain regions are attributed as a possible biomarker for schizophrenia (SZ). Diffusion tensor imaging (DTI) is used to capture WM tracts. Psychometric tests that evaluate the severity of symptoms of SZ are clinically used in the diagnosis process. In this study we investigate the correlates of scalar DTI measures, such as fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity with behavioral test scores. The correlations were found by different schemes: mean correlation with WM atlas regions and multiple regression of DTI values with test scores. The corpus callosum, superior longitudinal fasciculus right and inferior longitudinal fasciculus left were found to be having high correlations with test scores.
20 citations
TL;DR: Propagation of ictal epileptic discharges influences the clinical appearance of seizures and must be considered in the assessment of patients who have seizures with both temporal and occipital features.
Abstract: Propagation of ictal epileptic discharges influences the clinical appearance of seizures. Fast propagation from the occipital to temporal lobe has been well described, but until now the reverse direction of spread has not been emphasized. We describe two patients who experienced ictal propagation from temporal to occipital regions. One case presented with amaurosis during a seizure with temporal onset and temporal-occipital spread. In the second, temporal-occipital spread was documented during a seizure, which continued in the occipital lobe for six minutes. Depth electrode studies suggested the temporal ictal onset of seizures in both patients. Propagation from temporal to occipital lobe structures must be considered in the assessment of patients who have seizures with both temporal and occipital features. The propagation may have predictive value for their surgical outcome. The underlying anatomical structure might be the inferior longitudinal fasciculus.
10 citations
01 Jan 2008
TL;DR: It is found that patients with AD show demonstrable changes in vulnerable WM fiber pathways that likely reflect both retrogenesis and Wallerian degeneration (WM degeneration secondary to neuronal loss).
Abstract: The retrogenesis model of Alzheimer's disease (AD) posits that changes in white matter (WM) follow an inverse pattern of myelogenesis. Diffusion tensor imaging (DTI) was used to test the retrogenesis model. Specifically, greater loss of WM microstructural integrity (e.g., lower values of fractional anisotropy; FA) was predicted in late -myelinating WM fiber pathways (e.g., association pathways) in AD patients relative to healthy older adults, whereas early-myelinating fiber pathways (e.g., projection pathways) were not expected to show group differences. Furthermore, it has been proposed that AD includes a disconnection syndrome. Thus, higher cognitive functions dependent upon the synchronization of distributed neural networks (e.g., executive functions) were predicted to correlate with WM integrity. This study included 16 AD patients (mean age = 77.4, 64% female) and 14 demographically-matched healthy older adults (mean age = 77.3, 50% female). Image processing via tract-based spatial statistics (TBSS) was used to perform voxelwise statistics across subjects on FA skeleton maps. Additionally, region of interest (ROI) group comparisons were performed on early-myelinating (posterior limb of internal capsule, cerebral peduncles), late-myelinating (inferior longitudinal fasciculus, superior longitudinal fasciculus), and commissural (genu, splenium) fiber pathways. Permutation-based voxelwise analysis corrected for multiple comparisons revealed significantly lower FA values in AD patients compared to healthy older adults in late-myelinating association fiber pathways (superior longitudinal fasciculus, inferior longitudinal fasciculus, and uncinate fasciculus) and other fiber pathways that connect brain regions afflicted early by AD neuropathology (cingulum, fornix, splenium; p < .05). No significant differences were seen in early-myelinating pathways. These group differences remained significant after controlling for grey matter, WM, and white matter hyperintensity volumes. ROI analyses showed significantly lower FA in the inferior longitudinal fasciculus (p < .05). Pearson correlations revealed that dementia severity and neuropsychological composite scores in the domains of executive functions, processing speed, and memory were significantly related to WM integrity (p < .05). In conclusion, we found that patients with AD show demonstrable changes in vulnerable WM fiber pathways that likely reflect both retrogenesis and Wallerian degeneration (WM degeneration secondary to neuronal loss). WM integrity was associated with changes in higher-order cognition, supporting the view of AD as a disconnection syndrome. Knowledge of the pattern of WM microstructural changes in AD and its underlying mechanisms may contribute to earlier detection and intervention in at-risk groups
2 citations